Disposable diapers have met with increased commerical acceptance in recent years primarily because of their convenience, as opposed to cloth diapers, which must be laundered when soiled. Many different constructions have been proposed and some have been quite successful in the market place. However, even the more successful diapers are inadequate in certain functional aspects.
One design criterion which has been sought to be achieved is the desire to keep moisture away from the surface of the diaper which comes into contact with the infant's skin and thereby avoid skin irritation and infection.
A corollary criterion to this is the desire to retain moisture in the absorbent material, i.e. once the moisture has been drawn into the absorbent material and away from the infant, it must be prevented from migrating to and concentrating at the ends of the absorbent material which are close to or, sometimes, in contact with the infant and from which the moisture can seep into the bed clothes or outer garments of the infant.
Various inventions have been directed to distributing the moisture throughout the absorbent core, and directing it to the area of the core farthest from the infant's skin, however, these embodiments have failed to prevent the migration of moisture out of the ends of the diaper. Commonly assigned Mesek et al, U.S. Pat. No. 3,612,055 discloses several diaper constructions that function extremely well in keeping moisture away from an infant's skin, while at the same time handling a full volume discharge of urine.
These functions are accomplished by a multi-layer diaper comprising, in order a fibrous facing layer which is to be brought into contact with the infant's skin, a layer of highly porous, loosely compacted cellulosic batt, a paper-like densified, highly compacted cellulosic fibrous layer integral with the loosely compacted batt, and an impervious backing sheet adhered to the densified layer throughout the interface therebetween. The facing layer is of porous construction and its fibers have less wettability for water than the fibers of the loosely compacted batt, resulting in a tendency for liquid to flow from the facing web into the batt. The densified, fibrous layer has a smaller average pore size than the loosely compacted batt, resulting in a tendency for liquid to flow preferentially from the batt into the underlying densified layer rather than to other areas of the batt, thus contending to restrict wetting in the batt to an area of moderate size. Liquid flowing into the densified layer tends to spread through the densified layer because of its wetting action, and liquid which might pass through the densified layer during discharge (when flow is rapid) is held back by the impervious backing sheet for a sufficient time to permit absorption to take place. Liquid in excess of the absorptive capacity of the densified layer is forced back by the impervious layer into the dry portion of the loosely compacted batt, thus utilizing the additional absorptive capacity therein. In the preferred species in the above-mentioned patent, the paper-like, densified layer extends continuously over substantially the entire area of the loosely compacted batt. In the continuous, paper-like, densified layer the fluid flow is outwardly from the area of initial wetting and is substantially equal in all directions.
In absorbent panels including a continuous densified layer of uniform thickness, because of the equal flow rate in all directions, it is possible for fluid to migrate to the side edges of the densified layer before it reaches the longitudinal edges thereof, with resultant flow leakage at the sides of the product. Commonly assigned Repke U.S. Ser. No. 396,242, filed Sept. 11, 1973, a continuation-in-part of Repke U.S. Ser. No. 266,013, filed June 26, 1972, which was a continuation-in-part of Repke U.S. Ser. No. 187,239, filed Oct. 7, 1971, discloses an improvement upon the diaper structures disclosed in the Mesek et al patent by providing an absorbent panel that includes a highly porous, loosely compacted fibrous cellulosic batt with an integral, continuous, paper-like, densified cellulosic fibrous layer which, in selected longitudinally aligned areas, is thickened with additional densified cellulosic fibrous material. The thickened and unthickened portions of the densified layer portion of the absorbent panel cooperate with one another to provide for increased flow of fluid within the densified portions of the absorbent structure by reason of a greater cross sectional area therein, thereby tending to cause a greater amount of the fluid passing through the facing layer and striking the loosely compacted batt portion of the absorbent panel to flow preferentially into the densified layer portion and then throughout the densified layer portion toward its outer edges.
In one embodiment of the invention, the thickened portions of the densified layer are provided by spaced, parallel strips or lines of densified fibrous material that extend lengthwise of the structure. When the absorbent panel is wetted in the central zone of the batt portion and the fluid flows into the densified layer of the absorbent panel, the thickened portions in that region function to rapidly transport the fluid lengthwise of the structure away from the initial wetted region, while the densified bridging portions between the thickened portions cause the fluid to spread laterally outwardly at a rapid rate, thus causing the fluid to encounter additional thickened portions of densified material, with resulting increased longitudinal flow.
However, in absorbent panels including a continuous, densified layer of uniform thickness and densified longitudinal lines, because of the greater flow rate in the longitudinal direction, it is possible for fluid to migrate to and be concentrated at the ends of the densified layer before it can be transferred to parallel densified lines, with resultant fluid leakage at the longtudinal edges or ends of the product. Thus, both types of absorbent panels disclosed in the above-mentioned patent and applications have certain limitations.